The established technologies are either highly invasive, e. g. by directly accessing the intracranial volume, or require stationary application. The disadvantage of non-invasive treatments of neurological disorders like tDCS or TMS is that they cannot be applied outside of the hospital setting due to the lack of accessible and safe mobile devices for therapeutic purposes. The disadvantage of the established intracranial neurostimulation systems (DBS or RNS) is their invasiveness and the associated risks for the patients.
A possibility for reducing the invasiveness of the treatment is to position the electrodes between skull and scalp of a patient. Such extracranial brain stimulation via electrodes located between skull and scalp face the challenge that the current must pass through the low conducting skull resulting in a resistance much larger for an extracranial stimulator compared to intracranial stimulation. The resistance seen by the stimulator can be up to 40 times larger than for a cortical stimulator with electrodes placed directly on the surface of the cortex. The exact magnitude of the resistance depends on the local thickness of the skull, its local conductivity, on the electrode contact area, and on the quality of the contact between electrode and skull.
There exists a need for optimized electrodes and electrode pads for efficient stimulation of the patient's tissue. A tight contact between the contact areas of the electrodes and the tissue of the patient, in particular to non-planar bone, is important for avoiding contact faults due to increased contact-resistance and increased leakage currents. So far, the electrodes proposed in the past are not optimum.